1. Technical Field
The present invention relates to an optical filter and a method for manufacturing an optical filter.
2. Related Art
JP-A-2009-134028 (Patent Document 1) discloses an optical filter composed of a Fabry-Perot etalon filter (hereinafter referred to as etalon filter or simply referred to as etalon in some cases) having a pair of optical films which face each other via a predetermined gap.
The etalon filter disclosed in Patent Document 1 includes a first substrate and a second substrate which are held in parallel to each other, a first optical film (first reflection layer) formed on the first substrate, and a second optical film (second reflection layer) facing the first optical film with a predetermined gap and formed on the first substrate. Each of the first optical film and the second optical film constitutes a mirror. By causing multiple interference of light between the mirrors, only light in a predetermined wavelength range according to the length of the gap (gap amount) can be transmitted. Moreover, by variably controlling the gap amount, the wavelength range of light to be transmitted can be changed.
In the etalon filter disclosed in Patent Document 1, bonding films each containing a siloxane (Si—O) bond are used for the bonding of the first substrate to the second substrate. The accuracy of wavelength separation in the etalon filter is deeply associated with the accuracy of gap amount. Accordingly, for improving the performance of the etalon filter, the length of the gap between the first optical film and the second optical film needs to be controlled with a high degree of accuracy. As one factor of the accuracy, when the first substrate and the second substrate are bonded via the bonding films each containing the siloxane bond, it is important to assure parallelism between the substrates without inclining the substrates.
However, in Patent Document 1, for bonding the substrates using the bonding films, processes are needed such that for example, the bonding film formed on each of the substrates is activated by ultraviolet irradiation, oxygen plasma treatment, or the like, alignment of the substrates is performed, and a load is applied to each of the substrates. In these steps, a slight inclination of the substrate may occur.
As causes of the occurrence of inclination of the substrate, the following is considered as one of the causes: an inclination, a rounded portion, or the like is likely to be formed at an edge portion of the bonding film, and due to misalignment (bonding film misalignment) when the bonding film is partially formed on each of the substrates or due to substrate misalignment in a step of bonding the substrates together, the inclination or rounded portion of the edge portion of the bonding film induces non-uniform deformation of the bonding film by the load in bonding.